1. Field of the Invention
The invention relates to a method for forming an opening, and more particularly, to a method for forming an opening for damascene structures.
2. Description of the Prior Art
With the progress of the semiconductor industry, performance and economic factors of integrated circuit design and manufacture have caused the scale of devices of integrated circuits to be drastically reduced in size and increased in proximity on a chip. However, performance of integrated circuits not only depends on reliability of the devices, but also relies on metal interconnections used to transmit signals between the devices. Therefore, integrated circuit fabrication on semiconductor structures for ultra scale integration (ULSI) requires multiple levels of metal interconnections for electrically connecting the miniaturized semiconductor devices. To overcome difficulties in fabricating metal interconnection in multi-layer, the damascene structure has been extensively researched and developed. As the resistive coefficient of copper is lower than that of other metals, such as aluminum, and copper has the advantage of better electro-migration resistance while low-k material effectively reduces resistance-capacitance (RC) delay effects between metal interconnections, single copper damascene structure and copper damascene structures and low-k insulating materials have been widely used in fabrication of integrated circuits. Accordingly, the copper damascene process is taken as the technique that can solve metal interconnection problem of deep sub-half micro integrated circuits in the future.
It should be noted in the conventional art, the deposition of barrier layer is conducted while the hard mask is still disposed on the dielectric layer. As a result, the barrier layer not only covers the bottom of the opening and the sidewall of the dielectric layer, but also covers a portion of the hard mask. As the critical dimension of the fabrication decreases, the blocking of the hard mask significantly lowers the incident angle for the sputtering of the barrier layer, which creates great difficulty to form a barrier layer having continuous profile on the sidewall of the dielectric layer. The incontinuous profile of the barrier layer ultimately causes the electroplated copper metal to form voids and produces and lowers the performance of the damascene structure.